Counters are used in various electronic devices for converting physical quantities such as light intensity, sound intensity, time, etc. into a digital signal. For example, an image sensor captures images from incident light and includes an analog-to-digital converter (ADC) for converting analog signals from a pixel array into digital signals. The ADC includes one or more counters that counts according to a clock signal.
Operation speed and power consumption of the counter affects the performance of a device and/or a system including the counter. For example, a complementary metal oxide semiconductor (CMOS) image sensor includes a relatively large number of counters to convert analog signals, output column by column from an active pixel sensor array, into digital signals. The number of counters increases with higher resolution of the image sensor. In that case, the configuration, operation speed, and power consumption of the counters determine the performance of the image sensor.